Display device and driving device of light source therefor

ABSTRACT

A driving device is provided, which includes: a switching unit directly connected to a first voltage from a source external to the driving device; a transforming unit indirectly connected to the switching unit for transforming the first voltage into a second voltage and applying the second voltage to a light source; a signal transmitting unit indirectly connected to the switching unit and transmitting a driving voltage for driving the switching unit based on a control signal; and an inverter controller outputting the control signal to the signal transmitting unit.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a display device and a driving deviceof a light source thereof.

(b) Description of Related Art

An artificial light source, which is part of a backlight assembly, isoften implemented as a plurality of fluorescent lamps such as CCFLs(cold cathode fluorescent lamps) and EEFLs (external electrodefluorescent lamps) driven by an inverter. The inverter converts a DCvoltage into an AC voltage and applies the AC voltage to the lamps to beturned on. The inverter adjusts luminance of the lamps based on aluminance control signal to control the luminance of the LCD. Inaddition, inverter feedback controls the voltages applied to the lampsbased on the currents of the lamps.

For controlling a plurality of CCFLs, the backlight assembly alsoincludes a plurality of transformers connected to the lamps to apply ahigh voltage to a hot electrode of each CCFL, and a resistor sensingcurrents flowing through the CCFLs and connected between cold electrodesof the CCFLs and a ground. The sensed current is relative to the totalcurrent plus the current flowing through the cold electrode of eachCCFL. Thus, the operating states of the CCFLs are not exactly determinedin using the sensed current.

Display devices used for monitors of computers and television setsgenerally include self-emitting display devices such as organic lightemitting displays (OLEDs), vacuum fluorescent displays (VFDs), fieldemission displays (FEDs), and plasma panel displays (PDPs), andnon-emitting display devices such as liquid crystal displays (LCDs)requiring an external light source.

An LCD includes two panels provided with field-generating electrodes anda liquid crystal (LC) layer having dielectric anisotropy and interposedtherebetween. The field-generating electrodes that are supplied withelectric voltages generate electric field across the LC layer, and thelight transmittance of the liquid crystal layer varies depending on thestrength of the applied field, which can be controlled by the appliedvoltages. Accordingly, desired images are displayed by adjusting theapplied voltages.

The light for an LCD is provided by lamps equipped at the LCD, or may benatural light.

The lamps for the LCD, which is a part of a backlight assembly, usuallyinclude fluorescent lamps such as CCFLs (cold cathode fluorescent lamps)and EEFLs (external electrode fluorescent lamps) driven by an inverter.The inverter converts a DC voltage into an AC voltage and applies the ACvoltage to the lamps to be turned on. The inverter adjusts luminance ofthe lamps based on a luminance control signal to control the luminanceof the LCD. In addition, the inverter feedback controls the voltagesapplied to the lamps based on the currents of the lamps.

Since, for driving the LCD, the backlight assembly is directly suppliedwith an external AC voltage, that is, a high common power source of ahigh current of about 110V or 220V, the dangers of electric shock topeople and of lightning become large. Thus, to protect against thesedangers, the backlight assembly must be supplied with a separate DCvoltage of a high voltage and a low current separated from the commonpower source, which is transformed by a DC-DC converter. Due to theseparate DC-DC converter, the manufacturing cost and consumption powerare increased. In addition, the weight and size of the backlightassembly increase, thereby the design efficiency of the display devicesis decreased.

SUMMARY OF THE INVENTION

In an embodiment of the present invention, a driving device is provided,which includes: a switching unit directly connected to a first voltagefrom a source external to the driving device; a transforming unitindirectly connected to the switching unit for transforming the firstvoltage into a second voltage and applying the second voltage to a lightsource; a signal transmitting unit indirectly connected to the switchingunit and transmitting a driving voltage for driving the switching unitbased on a control signal; and an inverter controller outputting thecontrol signal to the signal transmitting unit.

The signal transmitting unit may be a pulse transforming unit.

The pulse transforming unit may include a pulse transformer and arectifier.

The signal transmitting unit may include a photocoupler.

The driving device may further include a capacitor connected to theswitching unit and the transforming unit and being charged or dischargedbased on the operation of the switching unit.

The driving device may further include a current sensing unit connectedto the transforming unit, sensing a current flowing through the lightsource, and supplying information with the respect to the current to theinverter controller.

The switching unit may include a first switching element including afirst input terminal connected to the first voltage, a first controlterminal connected to the signal transmitting unit, a first outputterminal connected to the transforming unit, a second switching elementincluding a second input terminal connected to the output terminal ofthe first switching element, a second control terminal connected to thesignal transmitting unit, and a second output terminal connected to aground.

The first and second switching elements may be turned on in turn.

The signal transmitting unit may include a first pulse transformerconnected to the first switching element and a second pulse transformerconnected to the second switching element.

The signal transmitting unit may include a first photocoupler connectedto the first switching element and a second photocoupler connected tothe second switching element.

The first and second switching elements may be MOS (metal oxide silicon)transistors.

In a further embodiment of the present invention, a driving device isprovided, which includes: a switching unit including an input terminaldirectly connected to a first voltage from a source external to thedriving device; a transforming unit connected to an output terminal ofthe switching unit and a light source; a signal transmitting unitconnected to a control terminal of the switching unit; and an invertercontroller outputting a control signal to the signal transmitting unit.The transforming unit includes a transformer member, and the switchingunit and the light source are indirectly connected to the transformermember; and the signal transmitting unit includes a signal transmittingmember, and the inverter controller and the switching unit areindirectly connected to each other through the signal transmittingmember to indirectly transmit the control signal from the invertercontroller to the switching unit.

The transformer member may include a primary coil connected to theswitching unit and a secondary coil connected to the light source.

The signal transmitting member may include a pulse transformer includinga primary coil connected to the inverter controller and a secondary coilconnected to the switching element, and a rectifier connected to thesecondary coil.

The signal transmitting member may be a photocoupler.

The driving device may further include a capacitor connected to theswitching element and the transforming unit.

In a still further embodiment of the present invention, a display deviceis provided, which includes: a plurality of pixels arranged in a matrix;at least one light source supplying light to the pixels; a switchingunit directly connected to a first voltage from a source external to thedisplay device; a transforming unit indirectly connected to theswitching unit for transforming the first voltage into a second voltageand applying the second voltage to the light source; a signaltransmitting unit indirectly connected to the switching unit andtransmitting a driving voltage for driving the switching unit based on acontrol signal; and an inverter controller outputting the control signalto the signal transmitting unit.

The signal transmitting unit may be a pulse transforming unit.

The pulse transforming unit may include a pulse transformer and arectifier.

The signal transmitting unit may include a photocoupler.

The display device may further include a capacitor connected to theswitching unit and the transforming unit, and being charged ordischarged based on the operation of the switching unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describing preferredembodiments thereof in detail with reference to the accompanyingdrawings, in which:

FIG. 1 is an exploded perspective view of an LCD according to anembodiment of the present invention;

FIG. 2 is a block diagram of a part of the LCD shown in FIG. 1;

FIG. 3 is an equivalent circuit diagram of a pixel of the LCD shown inFIG. 1;

FIG. 4 is a circuit diagram of an inverter according to an embodiment ofthe present invention;

FIG. 5 shows waveforms outputted from first and second output terminalsaccording to an embodiment of the present invention; and

FIG. 6 is a circuit diagram of an inverter according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of thepresent invention are shown.

In the drawings, the thickness of layers and regions are exaggerated forclarity. Like numerals refer to like elements throughout. It will beunderstood that when an element such as a layer, film, region,substrate, or panel is referred to as being “on” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

A liquid crystal display as an example of a display device and a drivingdevice of a light source for a liquid crystal display according toembodiments of the present invention will be described with reference tothe accompanying drawings.

A liquid crystal display according to an embodiment of the presentinvention will now be described in detail with reference to FIGS. 1 to3.

FIG. 1 is an exploded perspective view of an LCD according to anembodiment of the present invention, FIG. 2 is a block diagram of a partof the LCD shown in FIG. 1, and FIG. 3 is an equivalent circuit diagramof a pixel of the LCD shown in FIG. 1.

Referring to FIG. 1, an LCD according to an embodiment of the presentinvention includes a display module 350 including a display unit 330 anda backlight unit 900, and a pair of front and rear chassis 361 and 362,and a mold frame 366 containing and fixing the LC module 350.

The display unit 330 includes a display panel assembly 300, a pluralityof gate tape carrier packages (TCPs) or chip-on-film (COF) packages 410,and a plurality of data TCPs 510 attached to the display panel assembly300, and a gate printed circuit board (PCB) 450 and a data PCB 550attached to the gate and the data TCPs 410 and 510, respectively.

The display panel assembly 300 includes a lower panel 100, an upperpanel 200, and a liquid crystal layer 3 interposed therebetween as shownin FIG. 3. The display panel assembly 300 includes a plurality ofdisplay signal lines G1-Gn and D1-Dm and a plurality of pixels connectedthereto and arranged substantially in a matrix in a circuital view asshown in FIG. 2.

The display signal lines G1-Gn and D1-Dm are disposed on the lower panel100 and include a plurality of gate lines G1-Gn transmitting gatesignals (also referred to as “scanning signals”) and a plurality of datalines D1-Dm transmitting data signals. The gate lines G1-Gn extendsubstantially in a row direction and are substantially parallel to eachother, while the data lines D1-Dm extend substantially in a columndirection and are substantially parallel to each other.

Each pixel includes a switching element Q connected to the displaysignal lines G1-Gn and D1-Dm, and an LC capacitor C_(LC) and a storagecapacitor C_(ST) that are connected to the switching element Q. Thestorage capacitor C_(ST) may be omitted in other embodiments.

The switching element Q that may be implemented as a TFT is disposed onthe lower panel 100. The switching element Q has three terminals: acontrol terminal connected to one of the gate lines G1-Gn; an inputterminal connected to one of the data lines D1-Dm; and an outputterminal connected to the LC capacitor C_(LC) and the storage capacitorC_(ST).

The LC capacitor C_(LC) includes a pixel electrode 190 provided on thelower panel 100 and a common electrode 270 provided on an upper panel200 as two terminals. The LC layer 3 disposed between the two electrodes190 and 270 functions as a dielectric of the LC capacitor C_(LC). Thepixel electrode 190 is connected to the switching element Q, and thecommon electrode 270 is supplied with a common voltage Vcom and coversan entire surface of the upper panel 200. In other embodiments, thecommon electrode 270 may be provided on the lower panel 100, and bothelectrodes 190 and 270 may have shapes of bars or stripes.

The storage capacitor C_(ST) is an auxiliary capacitor for the LCcapacitor C_(LC). The storage capacitor C_(ST) includes the pixelelectrode 190 and a separate signal line, which is provided on the lowerpanel 100 and overlaps the pixel electrode 190 via an insulator, and issupplied with a predetermined voltage such as the common voltage Vcom.Alternatively, the storage capacitor C_(ST) includes the pixel electrode190 and an adjacent gate line called a previous gate line, whichoverlaps the pixel electrode 190 via an insulator.

For color display, each pixel uniquely represents one of primary colors(i.e., spatial division) or each pixel sequentially represents theprimary colors in turn (i.e., temporal division) such that a spatial ortemporal sum of the primary colors is recognized as a desired color. Anexample of a set of the primary colors includes red, green, and bluecolors. FIG. 2 shows an example of the spatial division in which eachpixel includes a color filter 230 representing one of the primary colorsin an area of the upper panel 200 facing the pixel electrode 190.Alternatively, the color filter 230 is provided on or under the pixelelectrode 190 on the lower panel 100.

One or more polarizers (not shown) are attached to at least one of thepanels 100 and 200.

Referring to FIGS. 1 and 2, the gray voltage generator 800 is disposedon the data PCB 550 and it generates two sets of gray voltages relatedto the transmittance of the pixels. The gray voltages in one set have apositive polarity with respect to the common voltage Vcom, while thosein the other set have a negative polarity with respect to the commonvoltage Vcom.

The gate driver 400 includes a plurality of integrated circuit (IC)chips mounted on the respective gate TCPs 410 attached on an edge of thelower panel 100 of the display panel assembly 300. The gate driver 400is connected to the gate lines G1-Gn of the panel assembly 300 throughsignal lines (not shown) formed on the gate TCPs 410 and synthesizes thegate-on voltage Von and the gate off voltage Voff from an externaldevice to generate gate signals for application to the gate lines G1-Gn.

The data driver 500 includes a plurality of IC chips mounted on therespective data TCPs 510 attached on another edge of the lower panel 100of the display panel assembly 300. The data driver 500 is connected tothe data lines D1-Dm of the panel assembly 300 through signal lines (notshown) formed on the data TCPs 510, and applies data voltages selectedfrom the gray voltages supplied from the gray voltage generator 800 tothe data lines D1-Dm.

According to another embodiment of the present invention, the IC chipsof the gate driver 400 or the data driver 500 are mounted on the lowerpanel 100. According to further another embodiment, one or both of thedrivers 400 and 500 are incorporated along with other elements into thelower panel 100. The gate PCB 450 and/or the gate TCPs 410 may beomitted in such embodiments.

The gate PCB 450 is attached on the gate TCPs 410 in parallel to thelower panel 100. A plurality of signal lines (not shown) and electronicelements may be mounted on the gate PCB 450.

The data PCB 550 is attached on the data TCPs 510 in parallel to thelower panel 100. A plurality of signal lines (not shown) and electronicelements may be mounted on the data PCB 450.

As shown in FIGS. 1 and 2, the backlight unit 900 includes lamp unit 960fixed to be spaced from the lower chassis 362 by a predetermineddistance, a plurality of optical members 910 disposed between thedisplay panel assembly 300 and the lamp unit 960 and treating light fromthe lamp unit 960, an inverter 920 controlling the lamp unit 960, and apower supply 970 supplying a supply voltage to the inverter 920.

The lamp unit 960 includes a plurality of lamps LP such as a fluorescentlamp, lamp holders 365 fixing and supporting the lamps LP at both endsof the respective lamps LP, a plurality of lamp fixers 364 preventingdamage to lamps LP in the case when the LCD is dropped, and a reflectivesheet 363 disposed entirely under all the lamps LP and reflecting thelight from the lamp unit 960 toward the display panel assembly

In the present embodiment, the lamps LP are CCFLs. Alternatively, thelamps LP may be EEFLs, light emitting devices (LEDs), or a flatfluorescent lamp. The number of lamps may be varied if necessary.

The inverter 920 may be mounted on a separate inverter PCB (not shown)or the gate PCB 450 or the data PCB 550. The inverter 920 will bedescribed in detail later.

The power supply 970 full-wave rectifies a common power source of about85V to 265V with a high current applied from the outside using a bridgerectifier, smoothing the rectified voltage using a capacitor to convertit to a voltage of about 380V, and applies the smoothed voltage to theinverter 920. The power supply 970 may include a PFC (power factorcorrection) device to improve the power efficiency. The power supply 970may be mounted on the inverter PCB or may be included in a voltagegenerator for generating a plurality of voltages and be mounted on aseparate PCB.

The optical member 910 includes a plurality of optical sheets 901 and aspread plate 902 disposed between the panel assembly 300 and the lampunit 960, guiding and diffusing light from the lamp unit 960 to thepanel assembly 300.

As shown in FIG. 1, the lamps LP are disposed under the lower panel 100,which is called a direct type of mounting. The spread plate 902 may besubstituted with a light guide (not shown) and the lamps LP may bedisposed near one or both sides of the light guide, which is called anedge type of mounting. Not shown in FIG. 1, a top case and a bottom caseare disposed on the top chassis 361 and under the lower chassis 362,respectively, to combine the top and bottom cases to complete the LCD.

The signal controller 600 controlling the drivers 400 and 500, etc., isdisposed on the data PCB 550 or the gate PCB 450.

Now, the operation of the LCD will be described in detail with referenceto FIGS. 1 to 3.

Referring to FIG. 1, the signal controller 600 is supplied with inputimage signals R, G, and B and input control signals controlling thedisplay thereof such as a vertical synchronization signal Vsync, ahorizontal synchronization signal Hsync, a main clock MCLK, and a dataenable signal DE, from an external graphics controller (not shown).After generating gate control signals CONT1 and data control signalsCONT2 and processing the image signals R, G, and B to be suitable forthe operation of the panel assembly 300 on the basis of the inputcontrol signals and the input image signals R, G, and B, the signalcontroller 600 provides the gate control signals CONT1 for the gatedriver 400 and the processed image signals DAT and the data controlsignals CONT2 for the data driver 500.

The gate control signals CONT1 include a scanning start signal STV forinstructing the gate driver 400 to start scanning, and at least a clocksignal for controlling the output time of the gate-on voltage Von. Thegate control signals CONT1 may further include an output enable signalOE for defining the duration of the gate-on voltage Von.

The data control signals CONT2 include a horizontal synchronizationstart signal STH for informing the data driver 500 of start of datatransmission for a group of pixels, a load signal LOAD for instructingthe data driver 500 to apply the data voltages to the data lines D1-Dm,and a data clock signal HCLK. The data control signal CONT2 may furtherinclude an inversion signal RVS for reversing the polarity of the datavoltages (with respect to the common voltage Vcom).

In response to the data control signals CONT2 from the signal controller600, the data driver 500 receives a packet of the image data DAT for thegroup of pixels from the signal controller 600, converts the image dataDAT into analog data voltages selected from the gray voltages suppliedfrom the gray voltage generator 800, and applies the data voltages tothe data lines D1-Dm.

The gate driver 400 applies the gate-on voltage Von to the gate lineG1-Gn in response to the gate control signals CONT1 from the signalcontroller 600, thereby turning on the switching elements Q connectedthereto. The data voltages applied to the data lines D1-Dm are suppliedto the pixels through the activated switching elements Q.

The difference between the data voltage and the common voltage Vcomapplied to a pixel is expressed as a charged voltage of the LC capacitorC_(LC), i.e., a pixel voltage. The liquid crystal molecules haveorientations depending on the magnitude of the pixel voltage.

The inverter 920 converts a voltage with a high current from the powersupply 970 into a voltage with a low current to apply to the lamp unit960. The lamp unit 960 is turned on or off based on the convertedvoltage to control the luminance of the lamp unit 960. In addition, theinverter 920 controls the lamp unit 960. The operation of the inverter920 will be described in detail later.

The light from the lamp unit 960 passes through the LC layer 3 thatexperiences the change of its polarization. The change of thepolarization is converted into that of light transmittance by thepolarizers.

By repeating this procedure by a unit of the horizontal period (which isdenoted by “1H” and is equal to one period of the horizontalsynchronization signal Hsync and the data enable signal DE), all gatelines G1-Gn are sequentially supplied with the gate-on voltage Vonduring a frame, thereby applying the data voltages to all pixels. Whenthe next frame starts after finishing one frame, the inversion controlsignal RVS applied to the data driver 500 is controlled such that thepolarity of the data voltages is reversed (which is referred to as“frame inversion”). The inversion control signal RVS may also becontrolled such that the polarity of the data voltages flowing in a dataline in one frame are reversed (for example, line inversion and dotinversion), or the polarity of the data voltages in one packet arereversed (for example, column inversion and dot inversion).

Now, an inverter according to an embodiment of the present inventionwill be described in detail with reference to FIG. 4.

FIG. 4 is a circuit diagram of an inverter according to an embodiment ofthe present invention.

Referring to FIG. 4, the inverter 920 includes an inverter controller921, a switching unit 922, a transformer 923 indirectly connecting theswitching unit 922 to a lamp corresponding to the lamp unit 960 (shownin FIG. 2), a current sensing unit 924 directly connected to the lampunit 960 and the inverter controller 921 through signal lines, and asignal transmitting unit 925 indirectly connecting the invertercontroller 921 to the switching unit 922.

The inverter controller 921 is connected to a voltage Vcc of about 5Vand a ground voltage GND1. The voltage Vcc and ground GND1 are high andlow voltages with a low current based on high and low supply voltageswith a low current, of which charge supplement capacities are finite,respectively.

The signal transmitting unit 925 includes a first signal transmitter 925a, a second signal transmitter 925 b, a resistor R3 connected to anoutput terminal A of the inverter controller 921 and the first signaltransmitter 925 a, a resistor R5 connected to the first signaltransmitter 925 a and the switching unit 922, a resistor R4 connected toan output terminal B of the inverter controller 921 and the secondsignal transmitter 925 b, and a resistor R6 connected to the secondsignal transmitter 925 b and the switching unit 922.

The structure of the first signal transmitter 925 a is the same as thatof the second signal transmitter 925 b, and only the structure of thefirst signal transmitter 925 a will be described.

The first signal transmitter 925 a includes a pulse transformer T2 and adiode D3 connected to both terminals of the pulse transformer T2.

The pulse transformer T2 includes a primary coil L11 directly connectedbetween the resistor R3 and the ground GND1 and a secondary coil L12indirectly connected to the primary coil L11, of which a terminal isconnected to the resistor R5 and a cathode of the diode D3, and anotherterminal is connected to an anode of the diode D3.

The switching unit 922 includes switching elements Q1 and Q2 connectedin series between a voltage Vdd and a ground voltage GND2. That is, theswitching element Q1 has an input terminal connected to the voltage Vdd,a control terminal connected to the resistor R5 of the signaltransmitting unit 925, and an output terminal connected to the secondarycoil L12 of the pulse transformer T2 and the anode terminal of the diodeD3. The switching element Q2 has an input terminal connected to theoutput terminal of the switching element Q1, a control terminalconnected to the resistor R6 of the signal transmitting unit 925, and anoutput terminal connected to the ground GND2. In the present embodiment,the switching elements Q1 and Q2 are MOS (metal oxide silicon)transistors. In other embodiments, other types of transistors can beused for the switching elements.

The voltage Vdd and ground GND2 are high and low voltages with a highcurrent based on high and low supply voltages with a high current, ofwhich charge supplement capacities are infinite, respectively, contraryto the voltage Vcc and the ground GND1.

The transformer 923 is a transformer T1 including a primary coil L1directly connected between the output terminal of the switching elementQ1 of the switching unit 922 and the ground GND2, and a secondary coilL2 indirectly connected to the primary coil L1 and directly connected tocorresponding lamps LP of the lamp unit 960.

The current sensing unit 924 includes a pair of diodes D1 and D2connected to the secondary coil L2 of the transformer 923 in a reversedirection to each other, a resistor R1 connected between the diode D2and the ground GND1, a resistor R2 connected to the diode D2 and acapacitor C2 connected between the resistor R2 and the ground GND1. Thediode D1 is connected in a reverse direction from the secondary coil L2to the ground GND1, and the diode D2 is connected in a forward directionfrom the secondary coil L2 of the transformer T1 to the resistor R1. Thesignal outputted from a common terminal of the diode D2 and the resistorR1 functions as a sensing signal of a voltage with respect to a currentflowing from the resistor R1 to be applied to the inverter controller921. One terminal of the resistor R1 is connected to the ground GND1.

A capacitor C1 is directly connected between the switching unit 922 andthe transformer 923.

Now, the operation of the inverter 920 will be described in detail.

The inverter controller 921 is supplied with a dimming control signal(not shown), and a backlight ON/OFF signal (not shown) controlling theinverter unit 920 generated by pulse-with modulating an externallyapplied DC control signal (not shown) of a predetermined level based ona sawtooth wave of a predetermined frequency applied from an oscillatingcircuit (not shown).

For controlling the switching unit 922 based on the ON/OFF signal andthe dimming control signal, the inverter controller 921 outputs twosignals S1 and S2, as shown by waveforms (a) and (b) in FIG. 5, throughthe first and second output terminals A and B connected to the signaltransmitting unit 922, respectively. The signals S1 and S2 have the sameperiod as each other, but are opposite in phases. At this time, thepulse widths and the periods of the signals S1 and S2 are defined on thebasis of the ON/OFF signal and the dimming control signal.

When the signals S1 and S2 are transmitted to the first and secondsignal transmitter 925 a and 925 b through the resistors R3 and R4,respectively, currents flow through the primary coils L11 and L21 of thepulse transformers T2 and T3 of the first and second signal transmitters925 a and 925 b, respectively. Thus, voltages are generated on thesecondary coils L12 and L22 based on the turn ratios defined by theprimary coils L11 and L21 and the secondary coils L12 and L22,respectively.

The respective diodes D3 and D4 connected to the secondary coils L12 andL22 function as half-wave rectifiers. Thus, the diodes D3 and D4half-wave rectify the signals of only the positive (+) polarity andtransmit the half-wave rectified signals to the switching elements Q1and Q2 of the switching unit 922 connected through the respectiveresistors R5 and R6.

At this time, preferably, the half-wave rectified signals applied to theswitching elements Q1 and Q2 have different phases, and the time periodwhen the half-wave rectified signals maintaining a high level thereofare not overlapped with each other.

The respective switching elements Q1 and Q2 are turned on or off inaccordance with the signals from the first and second signaltransmitters 925 a and 925 b. At this time, due to the phase differencesof the signals, the turned-on times of the switching elements Q1 and Q2are not overlapped with each other.

When the switching element Q1 of the switching unit 922 is turned onbased on the signal from the first signal transmitter 925 a, the voltageVdd from the power supply 970 is charged in the capacitor C1, and thenis applied to the primary coil L1 of the transformer 923. At this time,the switching element Q2 of the switching unit 922 is turned off.

Next, when the switching element Q2 of the switching unit 922 is turnedon based on the signal from the first signal transmitter 925 b, acurrent with respect to the charged voltage of the capacitor C1 flows tothe ground GND2 through the switching element Q2. At this time, theswitching element Q1 of the switching unit 922 is turned off.

When an AC voltage is applied to the primary coil L1 of the transformer923 by the operation of the switching unit 922, a voltage with anappropriate magnitude defined by a turn ratio of the primary coil L1 isinduced to the secondary coil L2. The induced voltage is applied to acorresponding lamp of the lamp unit 960 to light the lamp.

Because the primary coil L1 and the secondary coil L2 of the transformer923 are physically separated, though the high voltage Vdd of a highcurrent is applied to the primary coil L1, the generated voltage of thesecondary coil L2 is a voltage of a current lower than that of thevoltage Vdd. That is, the high voltage Vdd of the high current isapplied to only the elements between the secondary coils L12 and L22 ofthe first and second signal transmitters 925 a and 925 b and the primarycoil L1 of the transformer 923.

Meanwhile, the low current with respect to the generated voltage flowsthrough the current sensing unit 924. The diode D2 of the currentsensing unit 924 half-wave rectifies an AC current flowing through thesecondary coil L2 of the transformer T1. The half-wave rectified currentflows to the ground GND1 through the resistor R1. The diode D1 functionsas a pass for a current flowing from the ground GND1 to the secondarycoil L2 of the transformer T1.

Since the voltage applied to both terminals of the resistor R1 isproportional to the current applied to a corresponding lamp of the lampunit 960, a voltage of a common terminal of the resistor R1 and thediode D2 is applied to the inverter controller 921 as a current sensingsignal. The inverter controller 921 adjusts the level of the DC controlsignal based on the current sensing signal to vary the duty ratio of thedimming control signal, and thereby the frequency and period of the ACvoltage applied to the transformer 923 are varied, to constantlymaintain the current flowing through the lamp.

Without a separate DC-DC converter, the high voltage of the high currentfrom the power supply 970 is directly applied to the switching unit 922of the inverter 920, and the high voltage of the high current is alsoapplied to the transformer 923 through the switching unit 922 using thepulse transformers T2 and T3. Thus, the transformer 923 generates thevoltage of the low current to light the lamp of the lamp unit 960.

Now, an inverter according to another embodiment of the presentinvention will be described in detail with reference to FIG. 6.

FIG. 6 is a circuit diagram of an inverter according to anotherembodiment of the present invention.

An inverter shown in FIG. 6 is substantially the same as that shown inFIG. 4 except for a signal transmitting unit 926. In detail, the firstand the second signal transmitter 925 a and 925 b of the signaltransmitting unit 925 shown in FIG. 4 include the pulse transformers T2and T3, respectively, but first and second signal transmitter 926 a and926 b of a signal transmitting unit 926 shown in FIG. 6 includephotocouplers, respectively.

That is, the respective first and second signal transmitters 926 a and926 b include photo diodes PD1 and PD2 directly connected between avoltage Vcc and resistors R3 and R4, and resistors R7 and R8 and phototransistors PT1 and PT2 directly connected in series between the voltageVcc and a switching unit 922.

As described above referring to FIG. 4, the respective signals with thedifference phases outputted from first and second output terminals A andB of an inverter controller 921 are applied to the first and secondsignal transmitters 926 a and 926 b through the resistors R3 and R4.

The respective photo diodes PD1 and PD2 of the first and second signaltransmitters 926 a and 926 b are turned on or off based on the outputsignals of the inverter controller 921. At this time, the turned-ontimes of the photo diodes PD1 and PD2 are not overlapped with eachother.

When the respective photo diodes PD1 and PD2 are tuned on, light emitsfrom the photo diodes PD1 and PD2, and the corresponding phototransistors PT1 and PT2 are turned on by the light emitted from thephoto diodes PD1 and PD2. Thus, the voltage Vcc is applied to the inputterminals of the switching elements Q1 and Q2 of the switching unit 922through the resistors R5 and R6. That is, though the respective phototransistors PT1 and PT2 are not directly connected to the photo diodesPD1 and PD2, the photo transistors PT1 and PT2 operates by the lightfrom the photo diodes PD1 and PD2.

When the switching element 922 is operating as described above withreference to FIG. 4, and when an AC voltage is applied to a primary coilL1 of a transformer 922, a voltage with an appropriate magnitude definedby a turn ratio of the primary coil L1 is induced to the secondary coilL2. The induced voltage is applied to a corresponding lamp of the lampunit 960 to light the corresponding lamp.

In this case, the high voltage Vdd of the high current is applied toonly the elements between the secondary coils L12 and L22 of the firstand second signal transmitters 926 a and 926 b and the primary coil L1of the transformer 923.

Without a separate DC-DC converter, the high voltage of the high currentfrom the power supply 970 is directly applied to the switching unit 922of the inverter 920, and the high voltage of the high current is alsoapplied to the transformer 923 through the switching unit 922 using thephoto couplers PT1 and PT2. Thus, the transformer 923 generates thevoltage of the low current to light the lamp.

According to the embodiments of the present invention, the pulsetransformers and the photo couplers are used as the signal transmitters,but other devices transmitting the signals from the inverter controller921 to the switching elements 922 without separate signal lines, forexample lever shifters, may be used as the signal transmitters.

According to the present invention, without a separate AC-DC converter,the high voltage of the high current from the power supply is directlyapplied to the inverter. Thus, the manufacturing cost, size, and weightof the inverter are decreased and thereby the design efficiency isincreased.

In addition, the consumption power, electromagnetic interference, andnoise caused by the DC-DC converter are decreased. Moreover, heat due tothe DC-DC converter is decreased, and thereby the reliability of amanufactured product is improved.

While the present invention has been described in detail with referenceto the preferred embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but, on the contrary, isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims.

1. A driving device comprising: a switching unit directly connected to afirst voltage from a source external to the driving device; atransforming unit indirectly connected to the switching unit fortransforming the first voltage into a second voltage and applying thesecond voltage to a light source; a signal transmitting unit indirectlyconnected to the switching unit and transmitting a driving voltage fordriving the switching unit based on a control signal; and an invertercontroller outputting the control signal to the signal transmittingunit.
 2. The driving device of claim 1, wherein the signal transmittingunit is a pulse transforming unit.
 3. The driving device of claim 2,wherein the pulse transforming unit comprises a pulse transformer and arectifier.
 4. The driving device of claim 1, wherein the signaltransmitting unit comprises a photocoupler.
 5. The driving device ofclaim 1, further comprising a capacitor connected to the switching unitand the transforming unit and being charged or discharged based on theoperation of the switching unit.
 6. The driving device of claim 1,further comprising a current sensing unit connected to the transformingunit, sensing a current flowing through the light source, and supplyinginformation with respect to the current to the inverter controller. 7.The driving device of claim 1, wherein the switching unit comprises afirst switching element including a first input terminal connected tothe first voltage, a first control terminal connected to the signaltransmitting unit, and a first output terminal connected to thetransforming unit; and a second switching element including a secondinput terminal connected to the output terminal of the first switchingelement, a second control terminal connected to the signal transmittingunit, and a second output terminal connected to a ground.
 8. The drivingdevice of claim 7, wherein the first and second switching elements areturned on in turn.
 9. The driving device of claim 7, wherein the signaltransmitting unit comprises a first pulse transformer connected to thefirst switching element and a second pulse transformer connected to thesecond switching element.
 10. The driving device of claim 7, wherein thesignal transmitting unit comprises a first photocoupler connected to thefirst switching element and a second photocoupler connected to thesecond switching element.
 11. The driving device of claim 7, wherein thefirst and second switching elements are MOS (metal oxide silicon)transistors.
 12. A driving device comprising: a switching unit includingan input terminal directly connected to a first voltage from a sourceexternal to the driving device; a transforming unit connected to anoutput terminal of the switching unit and a light source; a signaltransmitting unit connected to a control terminal of the switching unit;and an inverter controller outputting a control signal to the signaltransmitting unit, wherein the transforming unit includes a transformermember, and the switching unit and the light source are indirectlyconnected to the transformer member, and the signal transmitting unitincludes a signal transmitting member, and the inverter controller andthe switching unit are indirectly connected to each other through thesignal transmitting member to indirectly transmit the control signalfrom the inverter controller to the switching unit.
 13. The drivingdevice of claim 12, wherein the transformer member comprises a primarycoil connected to the switching unit and a secondary coil connected tothe light source.
 14. The driving device of claim 12, wherein the signaltransmitting member comprises a pulse transformer including a primarycoil connected to the inverter controller, a secondary coil connected tothe switching element, and a rectifier connected to the secondary coil.15. The driving device of claim 12, wherein the signal transmittingmember comprises a photocoupler.
 16. The driving device of claim 12,further comprising a capacitor connected to the switching element andthe transforming unit.
 17. A display device comprising: a plurality ofpixels arranged in a matrix; at least one light source supplying lightto the pixels; a switching unit directly connected to a first voltagefrom a source external to the display device; a transforming unitindirectly connected to the switching unit for transforming the firstvoltage into a second voltage and applying the second voltage to thelight source; a signal transmitting unit indirectly connected to theswitching unit and transmitting a driving voltage for driving theswitching unit based on a control signal; and an inverter controlleroutputting the control signal to the signal transmitting unit.
 18. Thedisplay device of claim 17, wherein the signal transmitting unit is apulse transforming unit.
 19. The display device of claim 18, wherein thepulse transforming unit comprises a pulse transformer and a rectifier.20. The display device of claim 17, wherein the signal transmitting unitcomprises a photocoupler.
 21. The display device of claim 17, furthercomprising a capacitor connected to the switching unit and thetransforming unit and being charged or discharged based on the operationof the switching unit.